This invention is a surface that can simultaneously contain hundreds of individually-addressable encoded images. This surface has advantages for advertising signage, retail packaging, road-way signage and markers, novelty surfaces for notebooks and toys, theatrical effects, navigation, interior and exterior wall coverings, and other applications.
This invention makes use of a reflective surface that is strongly specular and which is curved in a manner that yields spatial gain relative to a diffuse reflector. This invention takes advantage of the localized nature of glint off of such a curved specular reflector. The characteristic of a diffuse reflector is that it scatters a beam of light over a great portion of the hemisphere in front of the illuminated surface and does not demonstrate localized glint. A piece of paper and a movie screen are examples of diffuse reflectors. In comparison, a specular surface reflects a beam of light into a more limited portion of the same hemisphere. A specular reflection is typically included in a small angular region surrounding the line that is at an equal angle, but when referenced to the reflector surface's normal is oppositely signed, to the angle of impinging light. A household mirror and a polished chrome automobile bumper are examples of specular reflectors.
Limitation in direction of reflection, that is, containing the reflected light to within a smaller spatial expanse than characteristic of diffuse surfaces, can provide a “spatial-gain” which suggests a reflectance that exceeds the reflectance possibility of any diffuse surface. This is true as long as the solid angles that encompass the possible positions of observation and illumination are limited to solid angles less than a complete hemisphere.
Understanding of this invention is assisted by comparing a white-painted flat surface with the specialized case of a flat mirror. (This special case is for concept elucidation only and is not otherwise necessarily related to the claims of this invention.) If a flat, diffuse, white-painted object is held in the sunlight, an observer sees light reflected from its surface over a large extent of viewing angles, nominally the entire hemisphere in front of the object. Therefore, when such an object is rotated, light from it can be seen over a wide range of angular movement.
However, if a flat specular mirror is considered under the same conditions, then nothing is seen except within a small angular region where the mirror directs a great flash to the eye of the observer. The flash comes from reflection simultaneously off of a large region of the flat mirror, if not off the entirety of the mirror. The flash within this narrow angular condition can easily be thousands of times brighter than when the same incident sunlight is reflected from the white paint.
If the flat specular mirror's surface is altered by giving it purposeful curvature, then the angular extent on the curved mirror within which the flash is observable increases, though the intensity decreases. But even the decreased brightness is still many times greater than the whitest flat paint or other diffuse reflector. The ratio of brightness is the “gain” of the reflectance surface. Also unlike the flat mirror, the specular reflection of a light source, artificial or sunlight, comes only from a small region of the curved mirror, termed the glint spot. This feature further differentiates this invention's surface from the flat mirror, and it sets up a condition for multi-image encoding. This invention utilizes an array of compound surface with the aforementioned effects of curved specular mirrors not only for brightness, but also for presentation of multiple encoded images. Each element cell of the array ensemble is a small mirror in itself, termed herein a “mirrorlette.” The reflection of glint can be modified for each location on each of the mirrorlettes in such a manner as to produce an image and/or optical effect that is the summation of contributions from all or part of the array of mirrorlettes.